I. Field of the Invention
The present invention generally relates to processes for purifying contaminated water. The present invention provides methods for purifying water, which may or may not contain long-chain organic acids, e.g., fatty acids, and oils. More specifically, the present invention is directed to methods for purifying contaminated water, e.g., waters containing suspended organic colloidal emulsions or suspensions such as effluents from meat processing plants, dairies, cheese processing plants, bakeries, chemical plants and petroleum plants and effluents, including raw sewage.
II. Description of the Background
Economical and efficient methods and apparatus for purifying contaminated water, particularly water containing fatty acids, have long been sought. Many industrial facilities, particularly facilities plagued with fatty acid waste, have long sought improved methods for purifying wastewater. Similarly, isolated industrial facilities, e.g., offshore oil rigs and remotely located research facilities, have long sought economical, energy efficient methods for purifying wastewater. Finally, as the dangers of cancer caused by chlorinated organics have become more apparent, methods of purification using reduced levels of chlorine and chlorides have become more desirable.
The use of water-insoluble metal hydroxides, e.g., aluminum and iron hydroxides, to entrap and remove contaminants has long been known. These hydroxides have been produced by the dissolution of aluminum and iron sulfates and chlorides to produce flocculants which would coagulate and entrap colloids, colors, microbes, bacteria and other impurities. The entrapped contaminants could then be separated with the hydroxide flocculants by filtration. While removing the undesirable contaminants, these methods, however, undesirably increased the sulfate and chloride content of the water.
A method and apparatus for achieving the desired purification without increasing the chloride and sulfate content of the water was disclosed in U.S. Pat. No. 4,802,991 by Miller. The '991 patent illustrated and described a method of water purification wherein fatty acids contaminating the water are combined with metallic ions released from electrodes during electrolysis to form hydrophobic, metallic soaps. According to the process described by Miller, bivalent or trivalent metal ions released from electrodes during electrolysis combine with the fatty acids to form an insoluble flocculant. In order to ensure continuous production of ions, the electrodes in the apparatus disclosed by Miller were disposed in a moving bed of solid, inert particles. Those solid particles were kept in motion by the flow of process water through the electrolysis chamber in order to continuously abrade and clean the electrode surfaces.
The flocculant, in turn, entrained or absorbed other impurities present in the contaminated water. Thus, the flocculant served as a transport medium to remove not only fatty acids, but also other impurities from the water. The flocculant and entrained impurities were directed to a flocculation/separation basin where the flocculant and entrained impurities were separated by flotation, leaving purified water for withdrawal from the basin.
The method and apparatus described by Miller in the '991 patent, while technically elegant, found only limited use. Systems employing iron electrodes, while functional, proved unacceptable due to the difficulty in removing ferrous hydroxide from the purified water. Systems employing aluminum electrodes were found to be uneconomical due to the high cost for both electrodes and labor incurred for replacement of spent electrodes. Another disadvantage of the system described in the '991 patent was the tendency for partially consumed electrodes to break off and cause an electrical short circuit, thus preventing full use of the electrode and increasing the cost of operation considerably. Accordingly, use of the method and apparatus disclosed in the '991 patent was restricted to applications where other methods were cost prohibitive.
Another method and apparatus for achieving the desired purification were disclosed in U.S. Pat. No. 5,558,755 by Gardner-Clayson, et al. The '755 patent illustrated and described a method of water purification including a fluidized bed of metallic particles disposed between a pair of electrodes and through which the contaminated water was flowed. The electrodes were comprised of non-consumable materials so that they would not require frequent replacement. The particles, on the other hand, were comprised of a consumable metal which, under the influence of an applied electric charge, introduced metallic ions into the contaminated water at a rate sufficient to form the required hydrophobic, metallic soaps. Thus, the metallic particles, were used up in the process.
The '755 patent solved many of the problems which had prevented commercial use of the process disclosed in the '991 patent. The particles were relatively inexpensive and, more importantly, easily replenished without requiring an expensive shutdown of the system. The process disclosed in the '755 patent, however, suffered from the same difficulty in removing ferrous hydroxide from the purified water when iron particles were used as the consumable metal. The process also required the continuous application of an external electrical power source to drive the reaction. Accordingly, the method and apparatus disclosed in the '755 patent was not suitable for use in remote locations.
Thus, the water purification industry has continued to seek new and improved methods for removing contaminants, including fatty acids, from water without increasing the chloride or sulfate content of the water, without producing undesirable ferrous hydroxide and without requiring the input of a continuous electrical current. Accordingly, there has been a long felt but unfulfilled need for more economical, more efficient and more convenient methods for purifying water, particularly in remote locations. The present invention solves those needs.